1. Field of the Invention
The present invention generally relates to measurement systems using the magnetic field generated by a ferromagnetic part to estimate magnitudes (speed, position, etc.) associated with a cyclic motion of this part. The present invention more specifically relates to measurements linked to a rotating motion of a ferromagnetic part.
2. Discussion of Prior Art
The use of magnetic field measurements to determine the rotation speed of an automobile vehicle wheel is known. For example, document EP-A-0828161 describes a detection method and device in which a magnetic sensor is placed close to the wheel to use a ferromagnetic signature thereof and to deduce its rotation speed therefrom. To decrease the influence of other magnetic sources close to the wheel (the chassis, the door, etc.), it is provided to perform a differential measurement of signals originating from several sensors placed close to the wheel. The field components originating from magnetic sources of fixed value placed nearby are thus eliminated.
It would be desirable to be able to extract information relative to the rotation of a ferromagnetic part (for example, the crankshaft, the camshaft, etc.) of an automobile vehicle motor by measurement of the magnetic field.
The angular position of the crankshaft or of the camshaft is currently determined by an optical encoder. Such an encoder must then be isolated from soils which would distort the measurements. This generates a complex implementation.
However, transposing magnetic systems known for wheels to the estimation of the motion of other vehicle elements, and especially to the analysis of the motion of rotating elements of the motor, is an issue, since variable magnetic fields, of non-negligible amplitude as compared with the magnetic field of the parts for which a rotation measurement is desired to be performed, disrupt the measurement.